There is a need for a simple quick method to determine control instructions for machines controlled by large quantities of calculated digital information. Such a machine is described in U.S. Pat. No. 4,675,582, hereby incorporated herein by reference, where a plurality of carriages are propelled independently by a system of synchronous linear motors. There is a need to be able to simply and quickly determine the control information for a first steady state operating condition and there is a need to be able to determine the control information required to transition from the first steady state condition to a second different condition while the machine continues to run; and there is a need to do the determining quickly on-line in response to changing conditions observed while operating the machine. For instance, a use for such a linear motor system is to power carriages in a film stretching tenter frame as described in more detail in U.S. patent application 07/209,910, hereby incorporated herein by reference, and the operating conditions of the machine need to be changed in response to the film characteristics observed as a result of the stretching operation. The control system for the tenter includes zones of control in the linear motor primary positioned along both sides of the tenter to electromagnetically engage synchronous secondaries attached to each independently powered pair of carriages. Discrete bits of control information comprising control instructions are stored in zone controller memories in the control system to repeatably develop the electromagnetic wave for each zone that is coordinated in time with the waves of the other zones to continuously propel the carriage pairs throughout the length of the tenter.
In the '582 patent, the linear synchronous motor control instructions for steady state and transition operation were derived from predetermined curves describing position versus time (t) in units of lambda versus T, where lambda=length of one pole pitch for an electrical phase and T=cycle time between secondaries entering the system. Analog equations for the curves were solved for phase as a function of discrete time intervals to determine the bits of information for three electrical phases to be stored in the memories of the zone controllers. For each whole lambda for a phase, there is a change in the binary instructions that will occur at some time T, calculated from the lambda vs t relationship. The information for a phase for a given zone memory can be expressed in a table of values of lambda versus t, where the value of lambda is shown in degrees, 180 degrees per lambda, and t is shown by some constant times T to equal seconds. This determination of data in degrees versus seconds, however, has been found to be less convenient to work with than the time in clock ticks from a central programmable time base for accessing the memory addresses, and the teeth of the three-phase primary structure which is the phase angle lowest common denominator for a six-step motor drive.
Obtaining this data by solving continuous, analog relationships describing the secondary position versus time has been found to be a time-consuming operation, sometimes requiring many minutes of computer time. This is particularly true when determining transition information, since unique curves must be developed for each of many carriages undergoing transition. All the data stored for the carriage profiles must be calculated. For example, for some applications this might amount to 750,000 individual values which when converted to bit patterns would amount to over 50,000,000 bits of data? These calculations are often required to be done during machine operation since transition often proceeds in several steps for significant speed ratio changes. A first step can be calculated off-line, but during the calculation time for subsequent steps, the product processed by the machine is often scrapped, so it is important that this time be minimized. Precalculating the data and downloading it from a storage disc is also a slow process requiring a large disk storage and does not lend itself to last minute changes in operating conditions.